The invention relates to a wafer transfer apparatus for transferring and compacting wafers stacked in an interspaced manner in a first holding device, e.g. a magazine, into a second holding device, which has a carrier device which is provided with two rollers which are arranged parallel to one another and can each be rotated about its longitudinal axis, the rollers are operatively connected to drive means by means of which the rollers can be arranged in a plurality of rotational positions, each roller is provided with a plurality of wafer receptacles extending over at least part of their circumference. The receptacles are arranged offset both in the longitudinal direction and in the circumferential direction of the roller and are arranged in segment portions of the circumference of the roller which extend essentially parallel to the longitudinal axis of the respective roller. The invention furthermore relates to a method for transferring and compacting wafers.
A wafer transfer apparatus is known, for example, from EP 0 496 006. This gives a description of an apparatus in which wafers are transferred from one or more wafer holders to a carrier which has at least one loading station and one unloading station, lifting means for raising the wafers, support means moveable between the carriers, and actuating members connected to the said support means. The actuating members are in the form of cylindrical rollers which are mounted rotatably at one end in the support means and, perpendicular to their axis, have slots for guiding and receiving the wafers. In the wafer holder, e.g. magazines, the wafers are stored in a stacked, interspaced manner. The spacing between each here generally amounts to a multiple of the thickness of the wafers. The wafers can be arranged much closer together on the carrier if the wafers are to be fed for further processing, e.g. to an oven for heating purposes. To enable this processing to be carried out as efficiently as possible, it is advantageous to arrange the wafer stacks from the individual holders in a more compact form on the carriers. The solution proposed in the patent mentioned is suitable for this purpose.
However, the apparatus has the disadvantage that it can only be used to combine just two wafer stacks one inside the other in an offset arrangement. In other words: compared with the original arrangement of the wafers, they can only be transferred with a maximum compaction of 1:2.
The object of the present invention is therefore to specify a measure by means of which at least twoxe2x80x94but preferably more than twoxe2x80x94wafer stacks can be stacked one inside the other by means of apparatuses or methods of the generic type in order to achieve compaction.
According to the invention, this object is achieved, in a transfer apparatus mentioned at the outset, by virtue of the fact that in at least three segment portions there are receptacles for wafers of in each case at least one wafer stack, at least a fourth segment portion is formed, in which there are receptacles for the simultaneous arrangement of wafers of at least three wafer stacks, receptacles of different segment portions of the respective roller being offset both in the longitudinal direction of the roller and in the circumferential direction of the roller, and there being, in the at least fourth segment portion, receptacles which are essentially in alignment in the circumferential direction of the roller with receptacles of the first three segment portions.
The invention is thus based on the idea of forming a basic sequence from a pattern by means of a number of receptacles corresponding at least to the compaction ratio, the said receptacles being offset both in the longitudinal and in the circumferential direction of the roller. This pattern is repeated several times, as seen in the longitudinal direction of the rollers. The number of repetitions preferably corresponds to the number of wafers present in one of the stacks to be compacted. As seen in the radial and in the circumferential direction of the rollers, receptacles for the wafers are thus arranged alternately in different segment portions. According to the invention, it is possible here to increase the compaction ratio of the wafer stack to be produced by increasing the number of segment portions on the circumference of the rollers. In particular, fourfold compaction can be achieved in this way.
The object is furthermore achieved by a method as described herein.
Preferred refinements of the invention will be found herein.
In the context of the invention, the word xe2x80x9ccompactionxe2x80x9d is intended to mean the ratio of the spacings of the wafers in their original stack (as arranged in the transport container) to the spacings of the wafers in the newly produced wafer stack. The compaction is generally a ratio 1:x, where x is a whole number. However, the word xe2x80x9ccompactionxe2x80x9d could also be understood to mean the number of initial stacks nested one within the other required to assemble a new wafer stack. With this definition too, a ratio 1:x, where x is a whole number, would be obtained, and x would be the number of initial stacks. It has proven advantageous if each roller has x+1, preferably x+2, segment portions. In order to be able to use the individual segment portions, the rollers should be able to assume a number of rotational positions corresponding to the number of segment portions.